1. Field of the Invention
The invention relates, in general, to refrigeration systems, especially those of the commercial type used in the refrigeration of display cases in supermarkets or similar establishments. In a more particular sense, the invention has reference to automatic controls utilizing an element or elements sensitive to an undesirable condition developing in a refrigerant, and effective under these circumstances to automatically elevate head pressure to a value that overcomes the sensed condition.
2. Description of the Prior Art
In a commercial refrigeration system of the type used in supermarkets or similar establishments, the condition known as "flashing" develops, not infrequently, in the liquid line extending from the condenser to one or more evaporators incorporated in the system. Desirably, a liquid seal, that is, refrigerant in a completely liquid state, should exist at the expansion valve of each evaporator of the system. Maintenance of the liquid seal prevents the "starving" of the expansion valve associated with each evaporator, that is to say, each evaporator should be supplied continuously with a steady flow of liquid refrigerant if it is to operate at peak efficiency. The existence of a vapor-liquid combination at the expansion valve results in a consequent, often serious reduction in the level of operating efficiency.
Heretofore, it has been proposed to increase the operating efficiency of the evaporators by prevention or minimizing of flashing and the starving of expansion valves. For example, U.S. Pat. No. 4,167,102 to Willitts, issued Sept. 11, 1979 and owned by the assignee of the present application, discloses means for preventing starving of the evaporators in a refrigeration system in which a saturated gaseous refrigerant is utilized for defrost purposes. And, in Willitts application Ser. No. 022,583 filed Mar. 21, 1979, now U.S. Pat. No. 4,231,229 also owned by the assignee of the present application, a means for controlling receiver pressures is disclosed, having among other purposes the prevention of starving of the expansion valves.
These devices are fully efficient for their intended applications, especially in that they attack and solve problems in systems utilizing a reverse flow of gaseous refrigerant ("hot gas", "cool gas", or a combination thereof). However, the present invention approaches the problem of flashing of the refrigerant and starving of the expansion valves in a different way. Hence, the present invention solves similar problems in a way that permits it to be used to advantage in systems in which the controls of the prior art do not function with an equivalent efficiency.